net: add back Buffers implementation which got lost along the way to the switchover to this package

Signed-off-by: deadprogram <ron@hybridgroup.com>

net.go

@@ -8,6 +8,7 @@ package net
 
 import (
 	"errors"
+	"io"
 	"time"
 )
 
@@ -318,3 +319,77 @@ var errClosed = errNetClosing{}
 // in another error, and should normally be tested using
 // errors.Is(err, net.ErrClosed).
 var ErrClosed error = errClosed
+
+// buffersWriter is the interface implemented by Conns that support a
+// "writev"-like batch write optimization.
+// writeBuffers should fully consume and write all chunks from the
+// provided Buffers, else it should report a non-nil error.
+type buffersWriter interface {
+	writeBuffers(*Buffers) (int64, error)
+}
+
+// Buffers contains zero or more runs of bytes to write.
+//
+// On certain machines, for certain types of connections, this is
+// optimized into an OS-specific batch write operation (such as
+// "writev").
+type Buffers [][]byte
+
+var (
+	_ io.WriterTo = (*Buffers)(nil)
+	_ io.Reader   = (*Buffers)(nil)
+)
+
+// WriteTo writes contents of the buffers to w.
+//
+// WriteTo implements [io.WriterTo] for [Buffers].
+//
+// WriteTo modifies the slice v as well as v[i] for 0 <= i < len(v),
+// but does not modify v[i][j] for any i, j.
+func (v *Buffers) WriteTo(w io.Writer) (n int64, err error) {
+	if wv, ok := w.(buffersWriter); ok {
+		return wv.writeBuffers(v)
+	}
+	for _, b := range *v {
+		nb, err := w.Write(b)
+		n += int64(nb)
+		if err != nil {
+			v.consume(n)
+			return n, err
+		}
+	}
+	v.consume(n)
+	return n, nil
+}
+
+// Read from the buffers.
+//
+// Read implements [io.Reader] for [Buffers].
+//
+// Read modifies the slice v as well as v[i] for 0 <= i < len(v),
+// but does not modify v[i][j] for any i, j.
+func (v *Buffers) Read(p []byte) (n int, err error) {
+	for len(p) > 0 && len(*v) > 0 {
+		n0 := copy(p, (*v)[0])
+		v.consume(int64(n0))
+		p = p[n0:]
+		n += n0
+	}
+	if len(*v) == 0 {
+		err = io.EOF
+	}
+	return
+}
+
+func (v *Buffers) consume(n int64) {
+	for len(*v) > 0 {
+		ln0 := int64(len((*v)[0]))
+		if ln0 > n {
+			(*v)[0] = (*v)[0][n:]
+			return
+		}
+		n -= ln0
+		(*v)[0] = nil
+		*v = (*v)[1:]
+	}
+}